This invention relates generally to improvements in apparatus and methods for aligning wheels on automotive vehicles; and, more particularly, it relates to apparatus and methods utilized in measuring and adjusting certain angular wheel relationships in front wheel alignment, especially toe-in and toe-out angles. Correct wheel toe in automotive vehicles has been found to be very important in prolonging tire life as well as vehicle steerability and controlability.
Toe is typically defined as the difference in distance between the front and the rear portions of the front wheel of a vehicle or angular displacement of the plane of a wheel (perpendicular to its turning axis) relative to a predetermined longitudinal vehicle axis. When the forwardmost portions of a pair of adjacent wheels are closer together than the rear portions of the wheels, they are commonly referred to as in a "toe-in" condition. When the rear portions of wheels are closer together than the front portions, the condition is commonly referred to as "toe-out". Most automotive vehicles are designed so that the front wheel toe angles can be adjusted by lengthening or shortening the tie rods of the vehicle's front wheel suspension.
Various devices and apparatus for measuring toe angles of wheels on automotive vehicles are commercially available. Prior art devices have included various apparatus for measuring the angle of deviation between a reference device extending between the front wheels of a vehicle and a reference plane formed by the front wheels. Some devices have included apparatus for projecting beams of light from devices affixed to front vehicle wheels to off-vehicle targets.
For example, prior art devices are generally used to align front vehicle wheels substantially without reference to or concern for the orientation of the rear wheels of the vehicle, and they generally fail to provide a centered steering wheel. This alignment technique has resulted from the erroneous assumption that the rear wheels of the vehicle were in substantially perfect alignment and that none of the following conditions existed: (1) toe in the rear wheels; (2) rear axle sideset; and (3) inter-axle misalignment, such as swung rear end, swayed vehicle frame, and diamond vehicle frame. Further, in the prior art no consideration was given to possible occurrence of front wheel intra-axle misalignment referred to as "knee-back" or "set back". All of these prior art and commercial devices have operational shortcomings, and these erroneous assumptions are substantial reasons therefore.
In actual practice and field experience with commercial embodiments of the prior art, it has typically been found that one or more of the above-mentioned disregarded conditions frequently exist in automotive vehicles and almost always in damaged ones. Thus, it can be seen that the prior art alignment techniques and apparatus had common shortcomings, primary among these were front toe alignment without reference to rear wheel orientation and intra-axle misalignment of front wheels. These shortcomings, as will be described below, prevent correct and accurate toe alignment in vehicles in a manner insuring the best tire life, vehicle controllability and safety.
The apparatus and technique of the invention have been designed to provide an alignment measuring system for vehicle wheel toe which utilizes both front and rear wheel orientation to facilitate toe adjustment for great tire life and driver safety and to provide an essentially centered steering wheel.
The present alignment device measures and facilitates adjustment of the front toe in each of the front wheels by determining the angular displacement of the front wheels with respect to a calculated thrust-line reference. This reference is calculated algebraically by determining the amount of toe displacement in each of the rear wheels and dividing this total by two. Thus, the front wheels can be aligned with the calculated rear wheel thrust-line to provide a centered steering wheel and essentially perfect tracking of the front wheels to the rear wheel thrust-line.
The present alignment device includes electronic circuitry which is mounted on replaceable printed circuit boards for electronically calculating the amount of toe in each wheel and visually displaying the amount of toe in each of the front wheels in relation to the calculated thrust-line reference. The electronic circuitry provides relatively economical means for automatically calculating toe angles and utilizing a minimum amount of power while providing a high degree of reliability in use.
The system, as a whole, has been designed for relatively easy assembly and can be maintained in operation without frequent repairs. Thus, overall labor and time is saved.
Further, the apparatus of the invention enables an operator practicing the method of the invention, after he has secured the apparatus to a vehicle, to position himself between elevated front vehicle wheels and conduct both the measuring and adjusting functions without leaving this position. The front and rear toe measurements can be readily viewed on the apparatus (no wall references are required) from this position as can the calculations relative thereto. Finally, the tie rod adjustments can ordinarily be made from this position.